Microphone environmental protection device

ABSTRACT

A device for protecting a microphone sensing surface, such as a diaphragm, from the detrimental effects of the ambient environment. The device incorporates a perforated surface to protect the microphone and in conjunction with a chamber volume creates an acoustic resonance in the 1 kHz to 20 kHz spectrum, which improves the microphone signal-to-noise ratio performance. The microphone is acoustically coupled to the chamber volume for sensing pressure of the ambient environment. There is no line of sight to the microphone sensing surface from the ambient environment, so that rain, wind and sand have no direct path to the microphone sensing surface. The perforations of the outer surface are small to prevent objects from contacting the microphone sensing surface via a direct path. Water drains from the chamber volume and does not become trapped if an embodiment of the invention is temporarily submerged so that the microphone returns to normal operation quickly.

REFERENCE TO RELATED APPLICATIONS

This is a continuation patent application of copending application Ser.No. 13/796,579, filed Mar. 12, 2013, entitled “Microphone EnvironmentalProtection Device”, which claimed benefit under 35 USC §119(e) ofprovisional application No. 61/751,527, filed Jan. 11, 2013, entitled“Microphone Environmental Protection Device”. The aforementionedapplications are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to devices used to protect microphones from theambient environment.

Description of Related Art

Microphone screens typically incorporate porous materials, such asfoamed material and metal mesh, to protect the microphone sensingsurface, such as a diaphragm from being damaged by objects, such asfingers, and to prevent wind noise. Inventions such as those describedin U.S. Pat. No. 7,496,208, U.S. Pat. No. 2,520,706 and U.S. Pat. No.3,154,171 illustrate such examples.

However, there are significant problems with using porous materials suchas foam. Foam and other similar porous materials become clogged withwater when submerged or subject to rain. Porous materials absorb andhold water, dirt and salt crystals which change the nature of the soundsensed by the microphone. High frequency sounds are attenuated;therefore, the microphone signal no longer provides an accuraterepresentation of sound in the ambient acoustic environment.

Microphones have inherent noise associated with them called“self-noise.” Even in a perfectly quiet ambient environment, microphoneswill generate electrical noise at their output. This noise is due to theself-noise of electrical amplifier components, such as the “Johnsonnoise” of resistances and “flicker noise” of transistors. The acousticaland mechanical damping of a microphone diaphragm also contributes to theself-noise of a microphone.

The “input referenced self-noise” (IRSN) of a microphone is theequivalent sound pressure level (SPL) that would generate the same noiseat the electrical leads as the total effective self-noise of themicrophone. The IRSN is typically described as an A-weighted value withunits of decibels sound pressure level, or dB SPL, which is a weightedaverage over a frequency band. However, the IRSN may also be describedas a dB SPL value at a single frequency.

Microphones with high self-noise can mask data, such as speech or music,when the data is at low levels. All other parameters being equal,microphones with lower self-noise are superior to microphones withhigher self-noise.

SUMMARY OF THE INVENTION

The present invention protects a microphone from rain, wind, dirt, saltcrystals and objects using a chamber having a perforated barrier.Fingers, vegetation, equipment and other objects are kept fromcontacting and damaging the microphone sensing surface, and a line ofsight path from the ambient environment to the microphone is prevented,so that small particles such as sand and dust, water and wind do notimpact directly on the microphone sensing surface or on an acoustic ventused to provide a waterproof barrier for the microphone. This providesimproved damage protection.

Acoustic amplification of sound may be provided, which can result in animprovement of the signal-to-noise ratio of the microphone outputsignal.

In one embodiment, the invention can be attached to a noise-defendingheadset ear cup. In this embodiment the microphone is used to sense thesound outside of the ear cup and the microphone signal is input to anelectronic processing circuit that is used to shape the signal andprovide amplification and/or attenuation of the signal. The processingcircuit signal output is input to an amplifier that is connected to aspeaker to generate sound in the ear cup. In this way, the user canmonitor ambient sounds and modify the amplitude and frequency content ofthe sounds to suit his/her needs. An embodiment of the invention mayalso be incorporated in manikins or other mechanical structures used tomimic the diffraction of sound around the human head.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a view of an embodiment of the invention as it would beincorporated into a vertical outer surface.

FIG. 2 is a view of the interior of an embodiment of the invention withthe perforated cover, screen and screws removed.

FIG. 3 is a cross-sectional view of an embodiment of the invention alongcut line B-B from FIG. 1.

FIG. 4 is a cross-sectional view of an embodiment of the invention alongcut line A-A from FIG. 1.

FIG. 5 is a view of an embodiment of the invention using slotperforations as it could be incorporated in an ear cup of a headset.

FIG. 6 is a view of an embodiment of the invention using circularperforations as it could be incorporated in an ear cup of a headset.

FIG. 7 is a view of an embodiment of the invention using a single slotperforation as it could be incorporated in an ear cup from a headset.

FIG. 8 is a plot of the improvement in acoustic response when anembodiment of the invention with slot perforations is incorporated in anear cup of a headset.

FIG. 9 is a cross-sectional view of an embodiment of the invention alongcut line C-C from FIG. 7.

FIG. 10 is a cross-sectional view of an embodiment of the inventionincorporating an auxiliary wind screen and drain tube.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

An embodiment of the invention is a device for protecting microphonesagainst environmental damage which incorporates a special perforatedbarrier on the outer surface of a chamber, which provides a line ofsight from outside the chamber volume to inside the chamber volume. Thecross-sectional area of the perforations are large enough that water caneasily pass through the barrier and the barrier is self-cleaned withrain or can be cleaned deliberately with a spray bottle. An outer layerof the barrier can be made of a solid rigid material, such as plastic ormetal, with slotted perforations backed by an inner layer of metal meshmaterial.

A drainage path can be provided for water and debris that accumulate inthe chamber volume. The water drain may be a path back through theperforated barrier, or a separated dedicated drain path can be provided.This allows the device to be self-cleaning during rain and easily toclean using a spray bottle.

The barrier in this embodiment is a rigid perforated surface forming achamber which creates an effective acoustic mass. The total volume ofthe chamber creates an effective acoustic compliance. The combination ofthese two elements in this embodiment of the invention creates anacoustic resonator that is preferably in the frequency range of 1 kHz to20 kHz.

Microphones have electronic and acoustic self noise. If the sound sensedby the microphone is increased, the effective signal-to-noise ratio ofthe microphone increases and yields an effectively quieter microphonesignal for the same ambient acoustic noise signal.

An equalizer circuit (active or passive) can be connected to the outputof the microphone to attenuate the frequency region of boosted signal.Therefore, because the microphone signal is attenuated, the self-noiseof the microphone is reduced. However, because the acoustic resonatoramplifies the sound through acoustical means, the measured signalstrength remains at the same amplitude. Therefore, the signal-to-noiseratio of the microphone output is increased by the resonator of anembodiment of the invention and the effective IRSN is reduced whichyields a higher quality microphone.

The microphone is located in a position relative to the chamber wherethere is no direct line of sight from the ambient environment outsidethe chamber to the sensing surface of the microphone. It will beunderstood that as used herein the phrase “no direct line of sight” isintended to mean that the sensing surface is located outside of, orspaced apart from, any imaginary sight line passing from the environmentthrough the chamber. In other words, it is the location and conformationof the chamber and its relationship to the sensing surface of themicrophone which provides the lack of line-of-sight from the environmentto the sensing surface, rather than the prior art arrangement of havingthe sensing surface facing the environment with only a physical barriersuch as a solid or foam or cloth cover providing the protection betweenthe sensing surface and the environment.

In this way, any wind, sand or rain that is blown into the chamberthrough the perforated barrier makes its first contact with the physicalstructure of the chamber, instead of the microphone sensing surface,which reduces the kinetic energy compared to an unobstructed path. Thishelps protect the microphone sensing surface, such as a diaphragm, whichcan be damaged by the force from direct impact of rain or objects.Microphones, such as condenser, MEMS, dynamic and piezoelectric employvarious types of sensing surfaces, such as single and multiplediaphragms and piezoelectric solids among others.

The microphone used in an embodiment of the invention is preferablywaterproof. However, an additional waterproof membrane, called anacoustic vent, can be incorporated to block the path to the microphonesensing surface to ensure that the microphone is not damaged by contactwith water. Acoustic vents may be attached directly to the front face ofa microphone or other locations, such as the end of a microphonecoupler, which would provide a water tight seal between the ambientenvironment and the microphone sensing surface.

FIG. 1 depicts a view of an embodiment of the invention as it would beincorporated into a vertical outer surface with “UP” indicating thedirection of higher altitude. A perforated cover 2 is attached to anouter surface 10, using flush-mounted screws 6. Alternatively, screwsmay be fastened from behind the outer surface so that the screws cannotbe seen from the perspective shown.

The perforated cover 2 incorporates at least one slot perforation 4having a length u and a height v. In a preferred embodiment, slotperforations are rounded at the ends and do not have sharp edges to helpminimize wind turbulence when wind blows across the outer surface 10.

Behind the slot perforations, a screen 8 is attached to the back of theperforated cover 2. The screen 8 is preferably made of wire and coatedwith an oleophobic coating that tends to repel oil and other fluids,although other coatings, such as hydrophobic coatings, may also be usedthat tend to repel water and other fluids. The screen 8 prevents objectslonger than slot length u from passing lengthwise through the slots.Alternatively, the screen 8 can be attached to the front of theperforated cover 2 to improve wind noise reduction.

A drain output 12 is located near the bottom of the perforated cover 2.The drain output 12 is incorporated to more easily allow water, dirt anddebris to drain out of the interior of an embodiment of the invention.The screen 8 does not cover the drain output 12, so that dirt and otherparticles that may pass through the screen 8 to exit the interior of anembodiment of the invention.

FIG. 2 is a view of the interior 24 portion of an embodiment of theinvention, with the perforated cover 2, screen 8 and screws 6 removed.Screw holes 14 are provided to receive the screws 6 that secure theperforated cover 2. A rectangular screen recess 16 is incorporated toprovide room for the screen 8 when the perforated cover 2 is attached.Within the interior 24 there is a chamber 20 with average width f andaverage height d (averages are used here because the interior isirregular).

At the upper end of the interior 24 is located a microphone coupler 18which is acoustically coupled to the chamber 20. The coupler 18 ispreferably made of elastomeric material such as molded silicone or othercompliant material.

The chamber 20 is enclosed by the interior structure and elements of anembodiment of the invention such that if water enters the chamberthrough the slot perforations 4 or drain output 12, the only path forwater to drain from the chamber is through slot perforations 4 and drainoutput 12.

Within the chamber 20 is a recessed drain channel 22 with width k. Therecessed drain channel 22 could be located as shown in the figure, or,alternatively could be centered, relative to dimension f, within thechamber 20. The drain channel 22 may incorporate other geometries, suchas an “hour glass” design where the drain channel becomes restricted inthe middle, relative to dimension d of chamber 20, while having greaterwidth at the top, where the microphone coupler 18 is located, and at thebottom, where the drain output 12 would be located. The “hour glass”design provides for larger diameter microphone couplers and draindiameters while minimizing the total chamber 20 volume.

FIG. 3 is a cross-sectional view of an embodiment of the invention alongthe cut line B-B from FIG. 1, cut through the length u of one of theslots 4. In this view of an embodiment of the invention, a portion ofthe chamber has a depth h while the drain channel 22 is recessed furtherby depth w. Preferably, depth h should be greater than 1 mm tofacilitate water drainage and prevent water retention. The interiorgeometry may be curved instead of the sharp edges shown in FIG. 3.

The drain channel 22 provides for improved draining of water from thechamber 20 but also allows room for incorporating larger diametermicrophones and microphone couplers 18 without increasing the totalchamber 20 volume appreciably. The drain channel is shown to one side ofthe chamber 20 but could as well be centered relative to dimension f, orplaced in other locations in the chamber 20.

The microphone coupler 18 has a coupler sound channel 30 that couplessound to an acoustic vent 26. The microphone coupler 18 in thisembodiment is located in the drain channel 22 because it is larger indiameter compared to h.

A cross-sectional view of the slot perforation 4 can be seen in FIG. 3with smooth contoured surfaces, such as a contour surface 33 facing theambient environment instead of sharp edges to minimize wind turbulenceand acoustic wind noise. The screen 8 has a mesh spacing z and a screendiameter q when the screen 8 incorporates cylindrical webbing such asmetal wire and is shown here attached to the back of the perforatedcover 2 to protect the screen 8 from damage. Alternatively, the screen 8can be attached to the front of the perforated cover 2 for improved windnoise reduction.

The perforated cover 2 is attached to an enclosure 32. The perforatedcover 2 and enclosure 32 define the chamber 20 volume. The enclosure 32extends to form the outer surface 10 in this embodiment. In anotherembodiment, the enclosure could be a separate component from the outersurface that attaches to the outer surface.

FIG. 4 is a cross-sectional view of an embodiment of the invention alongcut line A-A from FIG. 1, through the width v of the slots 4. The slots4 have a thickness c measured between inner edge 47 and outer surface51.

Wind turbulence causes undesirable acoustic noise. Preferably, the slots4 have smooth outer surfaces 51 instead of sharp edges to reduceturbulence due to wind when wind blows across the perforated cover 2.The slot 4 inner edges 47 do not cause appreciable turbulence becausewind is not blowing over this edge. However, the inner edge 47 may becontoured in alternative embodiments.

This cross-sectional view shows the microphone coupler 18 with ahorn-shaped coupler sound channel 30 (although other geometries may beused), attached to a microphone 40. Alternatively, the microphone 40 canbe completely or partially installed within the chamber 20 to minimizethe length of the coupler sound channel 30, or if desired the microphonecoupler 18 can be eliminated altogether. In the preferred embodiment,the microphone coupler 18 provides a water tight seal around themicrophone 40.

The coupler sound channel 30 couples sound from the chamber 20 to theacoustic vent 26. The acoustic vent 26 is gas permeable and couplessound to the microphone 40. The acoustic vent 26 is used to preventwater and dirt from impinging on a microphone sensing surface 42, suchas a fragile diaphragm. Preferably, the acoustic vent 26 is mounted tothe microphone 40 with an adhesive 44 to cover a microphone inlet 46 andcreates a water-tight seal.

As used herein, a “microphone inlet” is a perforation in a microphonehousing to allow sound to be coupled to a microphone sensing surfacefrom outside the microphone housing to inside the microphone housing. A“microphone sensing surface”, such as a diaphragm, typically vibrates inresponse to sound excitation, and this vibration is converted into anelectrical signal using various means known in the art.

Sound impinging on the exterior of the perforated cover 2 passes throughthe slots 4 and screen 8 and into the chamber 20, then through couplerinlet 48, coupler sound channel 30, acoustic vent 26 and microphoneinlet 46, where it is sensed by the microphone sensing surface 42.

The slotted perforated cover 2 helps protect the acoustic vent 26 fromrain, wind and sand as well as fingers and other foreign objects. Waterthat penetrates the perforated cover 2 runs down the chamber 20 and backout through the bottom slot perforations 4 and drain output 12. Thescreen 8 prevents objects smaller than the slot dimensions u and v fromentering the chamber 20. Objects smaller than the mesh spacing z ofscreen 8 can enter the chamber 20; however, they tend to fall to thebottom of the chamber 20.

The drain output 12 has diameter k that is larger than the mesh spacingz so that small objects the size of the mesh spacing z can exit thechamber 20 easily without being trapped. The drain output 12 is locatedat the bottom of the chamber 20 so that gravity tends to pull water outof the chamber 20 via the drain output 12. Thus, if any objects smallerthan mesh z do enter the chamber 20, water will wash the objects out ofthe chamber 20 through the drain output 12. In this way, an embodimentof the invention tends to be self-cleaning.

When an embodiment of the invention is used near an environment wheresalt spray is present, salt crystals will not become trapped as theywould if a porous foam material were incorporated. Any salt crystalsthat form from dried salt spray are also washed down the drain channel22 during the next rain, and will exit through the drain output 12.

The microphone 40 is located at the top of the chamber 20 so that anywater which might enter the microphone area will fall out of the couplersound channel 30 into the chamber 20 and exit out through the drainoutput 12. Because there are no porous materials within the chamber 20such as foam, water is not retained in the chamber 20.

The microphone 40 is also located at a position outside of or spacedapart from any imaginary straight line from the ambient environment tothe microphone sensing surface 42 or acoustic vent 26 (i.e there is “noline of sight”). That is, the microphone sensing surface 42 or acousticvent 26 is obscured by the geometry of the microphone coupler 18, thescreen 8 and the slot perforations 4. This is shown in FIG. 4 as line ofsight x. In this way, water spray and small objects cannot impact themicrophone sensing surface 42 through a direct path. The acoustic vent26 in this embodiment is also obscured and there is no line of sightfrom the environment to the vent 26.

The acoustic vent 26 may be incorporated in other locations in anembodiment of the invention, such as at the coupler inlet 48; however,care must be taken that there is no direct line of sight to the vent.

In the embodiment as shown in FIG. 4, there are multiple indirectunobscured lines of sight paths y from the ambient environment to theacoustic vent 26. Materials, such as many acoustic foams, that do nothave straight unobstructed paths through them tend to become cloggedwith water, dirt and salt crystals and need to be replaced regularly ifthey are used outdoors, whereas an embodiment of the invention describedherein is self-cleaning and, if desired, can be deliberately cleaned bythe user easily. In this embodiment, no material is used in the chamber20, and water easily drains from the chamber. However, highly porousmaterial can also drain water adequately if there are unobstructed pathsthrough the material, for water draining purposes, and the pores arerelatively large in size.

A microphone amplifier 36 is connected to microphone leads 38 to providebias circuitry and amplification. A passive or active electronicequalization circuit 34 can be connected to the microphone amplifier 36to create a generally flat frequency response to ambient sound for soundrecording or other purposes.

The perforated cover 2 and screen 8 are designed so that the acousticmass of the two, combined with the acoustic compliance of the chamber20, form a first acoustic resonance at a frequency between 1 kHz and 20kHz. The acoustic resonance amplifies the sound pressure in the chamber20, as compared to the ambient environment at and near the resonancefrequency. Boosting the sound pressure has the desired result ofimproving the effective IRSN of the microphone 40.

The acoustic compliance of the chamber 20 at room temperature iscalculated using the equation C_(a)=(Vol/1.42×10⁵) m⁵/N, where Vol isthe total volume of the chamber 20 in cubic meters (m³), m stands formeters and N stands for Newtons. The value of Vol is calculated usingthe equation Vol=edf m³, where e, d and fare the dimensions of thechamber 20 (see FIGS. 2 and 4), measured in meters.

Dimensions of 20 mm for d, 5 mm for e and 18 mm for f are an example ofa desirable geometry which yields a volume of 1.8 cc, and an acousticcompliance of 1.27×10⁻¹¹ m⁵/N. An average chamber depth e of greaterthan 1 mm is desirable to prevent water from becoming trapped within thechamber volume, and a slot width v of greater than 0.5 mm is desirableto prevent water from becoming trapped in the slots.

The acoustic mass of the perforated cover 2 and screen 8 will bedominated by the perforated cover 2 when the mesh diameter is smallcompared to the slot thickness c, and the mesh spacing z is similar insize to the slot width v.

The acoustic mass M_(a) of an individual slot or hole in kg/m⁴ isapproximated by the formula M_(a)=1.21 L/Area (ignoring end effects),where L is the thickness of the slots in meters, Area is the crosssectional area of the slots in square meters and Kg representskilograms.

An example of desirable dimensions for slot 4 would be 2 mm for thethickness c, and 18 mm for the length u and 1.5 mm for the width v,where c is the thickness, and there are four slots. The diameter of thewires of screen 8 mesh in this embodiment is preferably 0.4 mm while themesh spacing z is 0.8 mm.

Hence, the acoustic mass of a single slot of this geometry would beapproximated as 90 Kg/m⁴. The equivalent acoustic mass of a plurality ofslots of like geometry is equal to the acoustic mass of one slot dividedby the number of slots. Hence, the acoustic mass in this preferredembodiment would be approximated as 22.5 Kg/m⁴.

The acoustic resonance frequency of the resonator in Hertz (Hz) can becalculated by the formula:

$f_{0} = \frac{1}{\left( {6.28\sqrt{C_{a}M_{a}}} \right)}$

Using the values calculated above, the approximate resonance frequencyis 9,400 Hertz (9.4 kHz). However, end effects of the slots and thescreen result in higher acoustic mass due to the effective mass of theradiation impedance from the slots 4 and the acoustic mass of the screen8. End effects must be taken into account when the thickness of the slotis not large compared to the square root of the slot area and thecalculations become complicated for slots when the wavelength of thesound is not large compared to the slot length. The end effects also areaffected by how much edge contouring the designer uses for the slots.

Measurements of end effects for this geometry with a screen have beenmade in the Red Tail Hawk Corporation laboratory and yield an effectiveacoustic mass approximately four times as high as the calculatedacoustic mass. Hence, the resulting resonance frequency is approximately4.7 kHz for the design of this embodiment, rather than the calculated9.4 kHz.

In the preferred embodiment, the chamber 20 volume Vol is less than 2.32cc, so that a larger perforated area is not needed in the perforatedcover 2 to achieve higher resonance frequencies. A smaller sizedperforated area is easier to incorporate in devices such as headsetswith earcups that have limited space available.

An acoustic device is considered in the “lumped-element” region when allits dimensions are small relative to the acoustic wavelength inquestion. A device with resonance frequency below 1 kHz will tend toattenuate high frequencies if the slot or hole perforations are muchsmaller than a wavelength and the system acts as a lumped-element systemat higher frequencies. However, designs with resonances between 1 kHzand 20 kHz will transition out of the lumped-element region and will notattenuate high frequencies so long as the length of the slots is notsmall in relation to the wavelength of the sound wave.

The wavelength of a sound wave can be calculated as

$\lambda = \frac{s}{f}$where λ is the wavelength in meters, s is the speed of sound (343 m/sec)and f is the frequency in Hz. A slot of length of 1.8 cm corresponds toa wavelength of 19 kHz. However, the behavior of the slot begins totransition out of the lumped element region at around 1.9 kHz.

Acoustic systems that have geometries both small relative to thewavelengths of the acoustic wave and roughly equal to or greater thanthe size of the acoustic wave are difficult to analyze with simple mathand depend on the angle of acoustic wave incidence. A design, such asthe design of this embodiment, must be measured in the laboratory andtweaked to achieve the desired results.

FIG. 5 shows an embodiment of the invention as it can be incorporatedinto one of the two ear cups 64 of a headset (not shown). A second earcup (not shown), generally similar in geometry to the ear cup 64 shown,is typically employed in headsets, with the two earcups coupled by aheadband (not shown) attached to both ear cups. Headband attachments 66are provided on the ear cup 64 to mechanically attach a headband to theear cup 64.

In this embodiment of an embodiment of the invention, a perforated cover62 is attached to an outer surface 60 of the earcup, typically usingscrews (not shown) attached from inside the ear cup 64. In this way, thescrew heads cannot be seen from outside the ear cup 64. The enclosure ofan embodiment of the invention in this embodiment also forms the outersurface 60 of the ear cup 64. The perforated cover 62 follows thecontour of the outer surface 60 of the ear cup 64 to minimize windturbulence and wind noise. The perforated cover 62 employs slotperforations 76 a screen 72 attached to the front of the perforatedcover 62 and a drain output 70. When worn on the head, the drain output70 is located below the perforated slots 76 to facilitate waterdrainage. The drain output 70 in this embodiment is located on theperforated cover 62. The screen 72 does not cover the drain in thisembodiment.

A partition can be employed behind the enclosure of an embodiment of theinvention and within the ear cup to seal an embodiment of the inventionand all related circuitry to achieve a waterproof design. In this way,if the headset is submerged in water, no water will penetrate into thepartitioned volume. When an embodiment of the invention is incorporatedin the ear cup of a headset and the headset is used in wet conditions orsubmerged, no water damage is caused to the microphone or electronics,and because water drains from the chamber of an embodiment of theinvention quickly, normal microphone function is restored once theheadset is removed from the water.

FIG. 6 shows another embodiment of an embodiment of the invention as itcan be incorporated into one of the two ear cups 64 of a headset (notshown). Circle perforations 80 are employed instead of slot perforationsin this embodiment. A perforated cover 78 is attached to the outersurface 60 of the ear cup 64 using flush-mounted screws 76. A screen isnot employed, nor is a drain output in this embodiment. Water drainsfrom the circle perforations 80 if an embodiment of the invention getswet.

FIG. 7 shows another embodiment of an embodiment of the invention as itcan be incorporated into one of the two ear cups 84 of a headset (notshown). FIG. 9 shows a sectional view of the embodiment, cut throughlines C-C in FIG. 7.

In this embodiment, only a single slot perforation 86 is employed. Theperforated cover in this embodiment is molded into the ear cup 84 bodyitself. The earcup provides an outer surface 82. The enclosure of anembodiment of the invention in this embodiment is a separate componentthat is attached to the ear cup from inside the ear cup using screws,adhesive, ultrasonic welding or other means. A screen 76 is employed tokeep larger objects from penetrating into the chamber of an embodimentof the invention. Water drains through the single slot perforation 86and screen 76.

FIG. 9 is a cross-sectional view of an embodiment of the invention alongcut line C-C from FIG. 7, through the slot 86. In this embodiment themicrophone coupler 90 incorporates a coupler sound channel 92 that isshort and cylindrical in geometry, and the microphone coupler 90 is notmuch bigger than the microphone 40 in overall size. No acoustic vent isemployed in this embodiment, and the chamber 94 in this embodiment doesnot incorporate a recessed drain channel. There is no line of sight fromthe ambient environment to the microphone sensing surface 42 which helpsprotect the microphone sensing surface 42 from the direct impact ofblowing rain, sand and other objects. (For example, sighting along raytrace xx one cannot see the microphone sensing surface 42.) In thisembodiment, the microphone 40 used does not suffer from detrimentaleffects from exposure to water (waterproof design). If a non-waterproofdesign were incorporated in this embodiment, an acoustic vent 26 wouldbe used as a water bather for the microphone 40, for example, as shownin FIG. 3 and FIG. 4. There is an indirect unobstructed line of sight yyfrom the ambient environment to the microphone sensing surface 42. Thatis, there are no acoustic foams or other materials in the chamber 94that would block a path from the ambient environment to the microphonesensing surface 42 and tend to retain water.

FIG. 10 shows a cross-sectional view of an embodiment of the inventionincorporating an auxiliary wind screen 97, a drain tube 95 and a drainoutput 99. The auxiliary wind screen 97 can be attached to the outersurface 82. It may have a geometry that follows the contour of the outersurface 82 or may be bulbous or other geometries that reduce wind noise.

The auxiliary wind screen 97 can be constructed using mesh screen,cloth, gas-permeable membranes, foam or other materials that reduce windnoise but do not alter the acoustic audio-frequency sound sensed bymicrophone 40 in a detrimental way. The auxiliary wind screen 97 may bethin, for example when employing a single mesh screen or multiple meshscreen layers, or thick, for example when employing foam material with ahollow interior, or solid, for example when employing a solid piece offoam; other wind screen geometries may also be used.

The drain tube 95 is coupled to the chamber 94 and drain output 99 fordraining debris, water and/or other fluids into the ambient environment.Alternatively, the drain tube 95 could drain to the interiorenvironment, or other regions, instead of the ambient environment ifdesired.

FIG. 8 shows a plot depicting the difference in the response of amicrophone mounted flush on the outer surface of an ear cup compared tothe response of a microphone used in an embodiment of the invention inan ear cup with four slot perforations and similar aforementioneddimensions, at a range of audio frequencies. That is, the plot in FIG. 8shows a graph of the improvement in microphone sensitivity when using anembodiment of the invention compared to flush-mounting the microphone.

The plot is an average of three measurements from three differentincidence angles (front, side, back) for a plane pressure wave incidenton the ear cup when placed on an acoustic manikin in an anechoic room.The response shows a gain in sensitivity in the frequency range fromapproximately 1 kHz to 8 kHz. In this frequency band, thesignal-to-noise ratio has been improved by an embodiment of theinvention because the self-noise of the microphone alone has notchanged. The first resonance frequency of an embodiment of the inventionin this embodiment is approximately 4.7 kHz. There are other resonancesand antiresonances due to the headset geometry and invention above 4.7kHz.

Although there are several higher-frequency ranges where the response isattenuated, there is a significant net gain in output sensitivity due tothe resonance characteristics of an embodiment of the invention, whichresults in a significant net improvement in the IRSN.

Accordingly, it is to be understood that the embodiments of theinvention herein described are merely illustrative of the application ofthe principles of the invention. Reference herein to details of theillustrated embodiments is not intended to limit the scope of theclaims, which themselves recite those features regarded as essential tothe invention.

What is claimed is:
 1. An environmental protection device comprising: achamber comprising a plurality of sides enclosing a volume, one of theplurality of sides being formed by an outer surface of an earcup exposedto an ambient environment from which sound is to be detected by amicrophone, at least part of the outer surface forming a perforatedbarrier which is perforated by at least one perforation passing throughthe outer surface from an ambient environment into the chamber; themicrophone having a microphone sensing surface, located in an upperregion of the chamber, above at least one of the perforations; a draintube having a first end coupled to a lower region of the chamber and asecond end coupled to a drain output for draining fluids from thechamber into the ambient environment located in the outer surface belowa bottom of the perforated barrier; and wherein an acoustic mass of theperforated barrier combined with an acoustic compliance of the chamberforms an acoustic resonator amplifying the sound at the microphonesensing surface by acoustic means around a resonance frequency ofbetween 1 kHz and 8 kHz.
 2. The environmental protection device of claim1, in which the chamber has a volume of less than 2.32 cc and an averagechamber depth of more than 1 mm.
 3. The environmental protection deviceof claim 1, further comprising an auxiliary wind screen attached to theouter surface outside of the at least one perforation.
 4. Theenvironmental protection device of claim 3, in which the auxiliary windscreen has a geometry that follows a contour of the outer surface. 5.The environmental protection device of claim 3, in which the auxiliarywind screen is constructed of a material which reduces wind noise butdoes not alter the acoustic audio-frequency sound sensed by themicrophone.
 6. The environmental protection device of claim 3, in whichthe auxiliary wind screen is constructed of a material selected from agroup consisting of mesh screen, cloth, gas-permeable membrane and foam.7. The environmental protection device of claim 1, further comprising agas permeable acoustic vent arranged between the microphone sensingsurface and the chamber that restricts water from contacting themicrophone sensing surface.
 8. The environmental protection device ofclaim 7, in which there is an indirect unobstructed path from theambient environment to the gas permeable acoustic vent.
 9. Theenvironmental protection device of claim 1, in which there is anindirect unobstructed path from the ambient environment to themicrophone sensing surface.
 10. The environmental protection device ofclaim 1, further comprising an elastomeric microphone coupleracoustically coupling the chamber to the microphone sensing surface. 11.The environmental protection device of claim 1, in which the perforatedbarrier is formed by a plurality of slots passing through the outersurface.
 12. The environmental protection device of claim 11, in whichthe plurality of slots are greater than 0.5 mm in width.